The present invention is directed to electromagnetic signal handling, and especially to direction finding using electromagnetic signals. Prior art techniques and apparatuses for radio direction finding have involved a pair of vertically oriented loop antennas with orthogonal axes and an omnidirectional antenna, such as a sense antenna. Such techniques and apparatuses employed amplitude comparison direction finding to ascertain the angle of arrival of an electromagnetic signal.
A consequence of the requirement for several antennas and their related components in implementing prior art radio direction finding techniques is that the apparatuses for carrying out such prior art techniques are bulky. In the present market, smaller apparatuses are sought, so it is advantageous to be able to accomplish required operations using more compact apparatuses. Additionally, in the present market, it is advantageous to have systems that are more reliable in intense multipath environments.
Furthermore, typical systems for positioning and locating a transmitter often rely on range data gathered from a dispersed network of receivers. It is advantageous for a single receiving device to be able to locate a transmitter without relying on data from other receiving devices.
Similarly, existing receive systems employ “temporal rake” receivers that combine signal components received at different times to optimize reception of a received signal. It is advantageous for a receive system to be able to implement a “spatial rake” that selectively adds up signals arriving from different angles.
Also, conventional omni-directional receive systems are vulnerable to interfering signals arriving from particular directions. It is advantageous for a receive system to have the ability to receive signals omni-directionally yet decrease sensitivity to undesired or interfering signals arriving from particular directions. Similarly conventional omni-directional transmit systems may be prone to interfere with adjacent receivers lying in a particular direction. It is advantageous for a transmit system to have the ability to transmit signals omni-directionally yet decrease emissions in the particular direction of an adjacent receiver.
Finally, typical systems for intrusion detection using broadband radar systems rely on timing to yield a range gated detection perimeter. An intrusion may be detected at a particular range, but an exact position of an intruder is unknown. It is advantageous to have a system to identify the angle of arrival of a radar signal to precisely locate an intruder or other reflecting object.
There is a need for a more compact and more reliable apparatus for effecting radio direction finding operations to ascertain angle of arrival of electromagnetic signals at an antenna.